Urinary retention, a partial or complete inability to empty the bladder, can result from a variety of causes including benign prostatic hyperplasia (BHP), prostate cancer, bladder cancer, spinal cord injury, injuries of the urinary tract, urethral stricture, and urinary tract infection. If left untreated, urinary retention can have serious consequences for the patient including kidney failure. Therefore, patients with chronic or acute urinary retention usually require some type of intervention. A very common intervention is the insertion of an indwelling catheter, such as a Foley catheter, which provides a temporary conduit for draining the bladder. Because Foley catheters traverse the entire length of the urethra and include a segment that protrudes externally from the patient, these catheters are used only for temporary relief of acute or chronic urinary retention and especially for bladder drainage while patients are recovering from most types of surgeries.
Benign prostatic hyperplasia, the enlargement of the prostate gland, is the most common cause of bladder outlet obstruction. The prostate gland is about the size of a chestnut and surrounds the urethra just below the bladder neck. As men age, the prostate becomes larger, a process that constricts the urethra and obstructs the normal flow of urine from the bladder. Benign prostatic hyperplasia is very common and typically begins to develop in males older than 50. In fact, 60% of men over 60 and 95% of men over 80 experience bladder outlet obstruction due to BHP.
Surgical treatments are available which remove all or part of the prostate gland, thereby reducing or eliminating the urethral constriction and improving the patient's quality of life. These treatments include prostatectomy (open and laparoscopic), transurethral resection of the prostate (TURP), transurethral radiofrequency needle ablation (TUNA), transurethral microwave thermotherapy (TUMT), laser prostatectomy (LAP), and other experimental and emerging procedures. Open prostatectomy is the surgical removal of the inner portion of the prostate gland usually from a suprapubic or retropubic approach. Transurethral resection of the prostate (TURP) is considered the benchmark treatment for BHP and involves inserting a resectoscope and an electric loop to remove the obstructing tissue and to seal blood vessels. Transurethral radiofrequency needle ablation (TUNA) is a procedure in which low-level radiofrequency energy is delivered through needles to a localized area of the prostate, causing an increase in temperature, and inducing necrosis of prostatic tissue. Transurethral microwave thermotherapy (TUMT) uses microwave energy to heat prostatic tissue and simultaneously cools adjacent urethral tissue. Laser prostatectomy (LAP) is a minimally-invasive approach that uses laser-generated heat to vaporize or coagulate prostate tissue.
Recently, prostatic stents have been introduced as an alternative to surgical methods in the treatment of BHP. A prostatic stent, which was first developed in 1980, is a specialized urethral catheter that provides temporary or permanent relief of bladder outlet obstruction arising from BHP. The stents typically consist of a reinforced tubular section that spans the prostatic urethra, an anchoring means to keep it in place, and, in most cases, a tether for the removal of the stent. Unlike the Foley catheter, a prostatic stent does not typically include a section that extends externally from the patient. Prostatic stents are particularly useful for elderly patients or patients who are unable to undergo any of the typical surgical methods.
Several types of prostatic stents have been described in the prior art. Most of the early stent designs consist of a metal or plastic tube that spans the prostatic urethra providing an open conduit for urine drainage. For example, Rosenbluth, in U.S. Pat. Nos. 4,762,128 and 4,893,623 describes a metal prostatic stent that is deployed in the prostatic urethra via an inflatable balloon. These metal or plastic stents are not ideal for BHP because prostate and urethral tissue can become implanted in between the struts of the stent making them very difficult to remove without major surgery. In addition, these stents can lead to discomfort, inflammation, and infection. Other stent designs in the prior art consist of a plastic tube which spans, and is anchored within, the prostatic urethra. Even though these stents avoid the problems associated with metal stents, they can easily migrate or become dislodged, may cause discomfort for the patient, and may be difficult to remove. In addition, some of these stents are quite complex, expensive to make, and difficult to manufacture. Other anchoring methods have also been proposed for plastic stents that span the prostatic urethra, such as plastic stents with conical or flanged ends which are positioned immediately above and below the prostate so as to anchor the stent within the prostatic urethra.
In order to improve urinary drainage and patient comfort, other prostatic stent designs have been proposed. Unlike the previously mentioned designs, these stents span both the prostatic urethra and the external sphincter. Some of these stents do not have any anchoring means. As a result, there is a significant likelihood that these stents will migrate or become dislodged when voiding, cause discomfort, or leak due to the composition and dimension of the material that is placed in the narrow section that spans the external sphincter.
Since Foley catheters are used frequently to help with urine drainage, and since Foley catheters are equipped with an inflatable balloon that functions as an anchoring means within the bladder, many prostatic stent designs have adopted the inflatable balloon feature as well. For instance, Lazarovitz et al. in U.S. Pat. No. 6,716,252 describes a prostatic stent that spans the prostatic urethra and is equipped with an inflatable balloon which acts as an anchor within the bladder. This stent also includes a conical end that is placed immediately above the external sphincter which prevents the stent from migrating into the bladder. Whalen et al. in U.S. Pat. No. 7,141,038 describes a prostatic stent with a balloon anchor for the bladder, a compressible segment that spans the external sphincter, and another balloon that acts as an anchor in the penile urethra just below the external sphincter. This stent could be uncomfortable for the patient and would create severe problems and distress for the patient if either of the balloons malfunctioned.
Other recent prostatic stent designs include a balloon anchor for the bladder and another anchoring means immediately below the external sphincter in order to keep the stent properly positioned within the patient. For example, Whalen, et al., in U.S. Pat. Nos. 6,991,596 and 7,108,655 describe a prostatic stent with a balloon anchor in the bladder, a rigid section that spans the prostatic urethra, a series of threads that span the external sphincter, and an anchoring means immediately below the external sphincter. These stents are complex, expensive, and difficult to manufacture.